Known hollow building blocks are used to make reinforced concrete walls. In general these blocks are laid using staggered bond to ensure a good connection and to provide shear strength between the blocks. The hollow core of the wall is then filled with vertical steel reinforcing rods and concrete grout. A problem arises in aligning the blocks using staggered bond since they are not made with uniform height. Therefore, mortar is used between the blocks to accommodate this difference in height.
In order to eliminate mortar, Australian Patent No 692868 proposes the use of blocks having slotted ends, and keys to lock the ends of the blocks together. Additional courses are then added in stack bond, and the keys extend between adjacent courses so that each key locks four blocks in place. In the resulting structures there are vertically extending hollow voids to receive reinforcing steel and concrete. However, it is difficult to provide for horizontally arranged steel or horizontal concrete flow in such a wall.